PTL 1 discloses a medical screw 1 having a hollow hole, which is referred to as a cannulated screw as illustrated in FIG. 12. The screw 1 is used for joining a fracture site in a medical field in the related art, is provided with a screw thread portion 1b formed on an outer surface of a distal end portion 1a, is provided with a drill blade 1c formed at an extremity thereof, and is provided with a through hole 1d extending along a center axis along an entire length thereof. A rotational operating portion if formed of, for example, a hexagonal depression is provided at an entry of the through hole 1d of a head portion 1e of the screw 1, and the fracture site is joined by screwing the screw thread portion 1b into a bone by fitting a distal end portion of a driver-type rotational operation jig into the rotational operating portion if and rotating the same.
A procedure of screwing the screw 1 of the related art into the bone starts with piercing a metallic guide pin 2 through an incised skin A and a subcutaneous structure B in a fracture site D of a bone C substantially orthogonal to the fracture site D under anesthesia as illustrated in FIG. 13. A distal end of the guide pin 2 is pointed like a drill, is pieced through the skin A and the subcutaneous structure B as is, and is screwed into the bone C by being rotated by a motor or the like when the distal end comes into abutment with a bone cortex surface E of the bone C.
Subsequently, an upper end of the guide pin 2 is inserted into the through hole 1d on the distal end portion 1a side of the screw 1, and the screw 1 is pushed inward while being guided along the guide pin 2. The upper end of the guide pin 2 projected further upward from the head portion 1e of the screw 1 is inserted into a through hole 3b of a rotational operation jig 3. Subsequently, as illustrated in FIG. 14, the screw 1 is pushed inward of the skin A and the subcutaneous structure B by the rotational operation jig 3, and is rotated clockwise by a manual operation using a grip portion 3c of the rotational operation jig 3 after the distal end portion 1a of the screw 1 has come into abutment with the bone cortex surface E. With a rotation of the screw 1, the screw thread portion 1b is screwed into an interior of the bone C along the guide pin 2 while drilling the bone C with the drill blade 1c provided at the distal end thereof. The screw 1 may be screwed by the rotational operation jig 3 such as a medical electric drill or the like.
By screwing the screw 1 into the bone C while observing an X-ray TV monitor with radioscopy, the screw thread portion 1b penetrates through the fracture site D and starts unification. Then, as illustrated in FIG. 15, when the head portion 1e of the screw 1 reaches the bone cortex surface E, fixation of the fracture site D by the screw 1 is achieved.
The rotational operation jig 3 is pulled out from the guide pin 2, and finally, the guide pin 2 is withdrawn from the bone C, and then the skin A or the like is sutured, whereby a joining process on the fracture site D with the screw 1 is completed.
Since the fracture site D is united after an elapse of several months from the joining process, a process of withdrawing the screw 1 which has completed its role is performed. After the skin A and the subcutaneous structure B have incised, the screw 1 is taken out from the bone C by loosening the screw thread portion 1b, which is screwed in, by fitting a distal end portion 3a of the rotational operation jig 3 into the rotational operating portion if of the screw 1 and rotating the same counterclockwise. In this case, a withdrawal guide pin is preferably inserted into the screw 1 to guide the rotational operation jig 3 to the head portion 1e of the screw 1.
At a time when the fracture site D is unified by the fixation of the screw 1, callus is generated newly around the head portion 1e of the screw 1 in many cases, so that the head portion 1e of the screw 1 may be buried in the callus. In this case, since the callus becomes an obstacle which makes the rotational operation jig 3 difficult to fit into the rotational operating portion if of the screw 1, the callus needs to be removed.
The screw thread portion 1b of the screw 1 is pulled out from the bone C by rotating the rotational operation jig 3 counterclockwise after the rotational operation jig 3 is fitted correctly into the rotational operating portion 1f. At the time of being pulled out, the screw 1 is moved upward by a reaction force of the bone C until the screw thread portion 1b screwed into the bone C reaches the bone cortex surface E. However, in the case where the screw 1 is still buried in the subcutaneous structure B, the screw thread portion 1b runs idle and thus puling out of the screw 1 becomes difficult.
In the case where the screw 1 comes off the bone C when screwing the screw 1 at the time of joining the fracture site D and thus is screwed into the subcutaneous structure B as well, the screw 1 needs to be pulled out once to retry screwing. At this time, even though the screw 1 is rotated counterclockwise, the screw thread portion 1b runs idle and thus the screw 1 cannot be pulled out.
Furthermore, if several months have been elapsed from the joining process, the bone C having the screw 1 screwed therein may reject the metal, and thus a gap may be formed between the bone C and the screw 1. In such a case as well, the screw thread portion 1b runs idle and thus cannot be pulled out easily even though the screw 1 is rotated.
PTL 2 discloses an orthopedic screw having the same function as the medical screw 1, and describes that a reverse internal thread portion having a thread in a reverse direction to a direction of the screw thread formed at the distal end portion, is formed inside a head portion of the orthopedic screw, and the screw is pulled out by engaging an operating jig with the reverse internal thread portion and rotating the screw in a reverse thread direction.
The screw can be pulled out easily by using this orthopedic screw, because a withdrawal operating jig is integrated with the orthopedic screw via the reverse internal thread portion and the screw thread can be loosened from the bone by rotating the operating jig in the reverse direction.